EastEnders: E20' is a 13-part series about four new characters who move into Albert Square, but will include storylines and cameos by actors in the main programme.

The newcomers will play the roles of Fatboy, Leon Small, Mercy Olubunmi and Zsa Zsa Carter, who crash into Albert Square seeking solace from family life.

The online drama, created by a team of new London writers aged between 17 and 22, will go live in January next year ahead of the soap's 25th anniversary in February.

Episodes will be posted on the EastEnders website after 'EastEnders' TV episodes and will last between six and 12 minutes.

Squatting together in 89b George Street the secrets that drove the teenage characters from home will slowly be revealed and their shared problems will cement their friendship.

Ricky Norwood will play Fatboy, who has invented a number of personas since the age of seven in an attempt to escape his real identity, Arthur Chubb.

Norwood said: "It's an honour to now be part of a show that has been on in my house for as long as I have been alive. I am born and bred in the East End – a stone's throw from the real Albert Square – it fells like a homecoming. I love being part of a cast that feels like family and can't wait to have a scene in the Vic."

Leon, played by Sam Attwater, is described as a sexy and cool boxer with a short fuse and a lack of respect for those in authority.

His mother died when he was young and he takes a lot of responsibility for his alcoholic father.

Attwater said: "It is a great privilege to be working with such great actors and on such an established show. It's an amazing opportunity and I'm really enjoying tackling a character like Leon who has so much going on."

Mercy, played by the actress Bunmi Mojekwu, lives with her strict grandmother from whom she is harbouring a secret, and feels abandoned when her parents return to Nigeria.

Mojekwu said: "I feel so blessed to be a part of EastEnders: E20. My first day on set was just crazy, I was on Albert Square – a dream come true – I am enjoying every second."

Zsa Zsa, played by the actor and writer Emer Kenny, is a bright, funky and outspoken tomboy, similar to her aunt Shirley Carter, played by Linda Henry, an existing character in the BBC One show.

Kenny, who was one of the 13 writers of EastEnders: E20, said: "Kids these days use their laptops more than their televisions, so it's really exciting to be a part of a project that's taking drama online and connecting with these viewers."

Executive producer Diederick Santer said: "Not content with having E20 written by new writers, and our theme tune remixed by the audience, we've now found four talented newcomers from London to front the show. Emer, Bunmi, Ricky and Sam are brilliant young performers, noisy and fun."

Deborah Sathe, producer of EastEnders: E20, said: "It is so exciting to see these four young Londoners collide with the residents of Walford. The E20 site really celebrates these characters to the max and there will be lots of added extras!"

Viewers have been promised "crossover treats," both in the web series and the BBC One soap.

Channel 4 has used the spin-off format with its early evening teen soap 'Hollyoaks', creating post-watershed TV specials targeting an older audience with more daring storylines.

Fatboy, Leon and Zsa Zsa will also be seen on screen in EastEnders on BBC One from January.